A. Field of the Invention
This invention relates to the field of lightweight flowable and shearable materials including materials for cushions and padding, such as seat cushions or bed pads, where skin comfort and skin preservation are important. More particularly, this invention relates to a composite mixture of a lubricant and spherical objects which may be encased within a flexible container or sack and used as a cushion or padding. The exterior surfaces of the spherical objects are lightly lubricated to accommodate flow and shear, but lubricant is not used in an amount sufficient to cause dispersion of the spherical objects in the lubricant. Additionally, the mixture is adapted to minimize memory which would cause it to move, flow or change shape when a deforming force is removed. The composite mixture has a very low specific gravity, making it excellent for use with lightweight vehicles such as wheelchairs and bicycles, and which makes it an excellent flotation material.
B. The Background Art
In the prior art there has been substantial difficulty in designing padding or cushioning for contact with a patient's skin that has some or all of the following characteristics: (i) equalization of pressure across the entire area of skin contacted in order to prevent skin damage, (ii) readily flowable, (iii) low shearing force threshold, (iv) no or minimal memory, (v) low specific gravity, (vi) lightweight, and (vii) comprising a flowable material which has some or all of the following characteristics: (a) capable of being contained in a flexible, elastic bladder without leakage, (b) does not substantially vary in performance with temperature, (c) does not break down or separate into its constituent components over time, (d) does not feel overly cold to the touch, and (e) quickly warms to body temperature. The prior art has also been unable to design a flotation material which has a low specific gravity for buoyancy but is not stiff or semi-rigid and, therefore, somewhat uncomfortable for the wearer of a life vest containing such material.
For example, the typical prior art wheelchair seat consists of a fabric sling stretched between two metal bars on which the patient sits. Frequently the sling has a plastic or rubber coating for durability. Sling seats such as these are unable to conform to the shape of the human body, resulting in greater force being applied to some portions of the patient's anatomy than to others. Over time, high spots or bony areas on the patient's body often develop decubitus ulcers (pressure sores) or other tissue damage. Sling seats typically also have a high shearing force threshold, being resistent to movement or turning in response to movement by the patient. As the patient turns or moves within the seat, friction with the patient's body would tend to move the portion of the seat in direct contact with the patient's body. All portions of the typical seat, however, are typically held fast together, whether by monolithic construction, such as in foam seats, with stitching as in sling seats, or otherwise. The resulting high shearing force threshold causes tissue damage during turning or movement. Tissue damage from shear-resistant seats can be cumulative and debilitating over time. Foams and other traditional types of cushions and padding have provided little relief from the disadvantages of sling seats. For example, patients confined to bed typically experience the same skin damage as those using a sling seat even though mattresses usually include a combination of metal springs, foam padding and cotton or synthetic batting.
The previous solution to the problems of typical cushions and padding has been the use of gels or viscous and slimy liquids (hereinafter "fluid") contained within a flexible bag or bladder. The use of fluid within a flexible bladder for contact with a patient's body achieves much more uniform force or pressure on irregular body surfaces than traditional cushions and padding. The shearing force threshold of fluid within a bladder may be lower than in other cushions or pads because the bladder surface closest to the patient's body is free, within certain limits, to move with the patient's body as the patient moves. The bladder walls are not anchored to the gel so that as the patient moves, the bladder may move with respect to the gel. The fluid also has some ability to shear with respect to itself. The result is a seat which is less damaging to human skin than a typical sling seat. Unfortunately, most viscous fluids are very slow to respond to body movement, giving an undesirably high shearing force during quick body movement and failing to fully preserve the integrity of the patient's skin. Fluid within a bladder is currently used as padding in some wheelchair and bicycle seats. Such fluids are also very heavy, even when hollow microbeads are dispersed in the fluid. Further, prior art fluids flow under their own weight, causing them to exert a "head pressure" on bony protuberances of the body, causing skin damage and discomfort. Some prior art fluids also have memory, thereby exerting a force on bony protuberances of the body as the fluids try to return to shape; memory increases the likelihood of tissue damage.
Fluid has the disadvantage of being much heavier than the flexible foam used in typical cushions. Fluids commonly used in cushioning have specific gravities of 0.6 to 1.2, whereas a typical cushion foam may have a specific gravity of only 0.05 to 0.10. Thus, in order to achieve a lightweight seat, fluid must be used sparingly. When fluid is used sparingly, its positive characteristics are minimized. Use of gels in sufficient quantity to achieve the desired effect results in a seat weight unacceptable for many applications. For example, patients using wheelchairs commonly suffer from a weakened physical condition, and an increase in the weight of a wheelchair by only a few pounds can make it excessively burdensome for the patient to use. As another example, total bicycle weight is typically a primary consideration in the design of both road bikes and mountain bikes. The additional weight of a fluid seat is often unacceptable to all but the most casual of riders.
Another disadvantage of such gels is that they have a high thermal mass and a high coefficient of heat transfer. As a result, fluid seats typically feel cold to the touch, providing initial discomfort to the user and remain cold for long periods of time before warming. Fluids used in cushioning also exhibit substantial viscosity changes with temperature, causing them to become more viscous and lose their functional characteristics in cold temperatures. Similarly, in very warm temperatures, such fluids will exhibit excessive flow characteristics and again will not function as desired. Finally, fluids used in cushioning which have hollow microspheres dispersed therein will tend to break down and separate into their constituent components over time, causing a loss of functional characteristics. The user of such a fluid cushion must, therefore, periodically knead the cushion to re-mix the components of the fluid and keep it functioning. Kneading a fluid cushion can be difficult or impossible for many wheelchair users because of the hand strength required, which makes a fluid cushion very undesirable.
Terrence M. Drew et al. U.S. Pat. Nos. 5,093,138 issued Mar. 3, 1992 and 5,100,712, issued Mar. 31, 1992 describe a flowable, pressure compensating composition including water, a material for increasing the viscosity of water, and spherical particles dispersed throughout the volume of the water. Both of these patents are hereby incorporated by reference in their entirety. The composition disclosed in these patents is a deformable fluid which has the disadvantages of substantial weight, memory, and being slow to flow or shear in response to a deforming pressure and, thus, being prone to cause skin damage.
Chris A. Hanson U.S. Pat. Nos. 5,059,291 issued Oct. 22, 1991 and 4,952,439, issued Aug. 28, 1990 describe padding devices which are resistant to flow in response to an instantly applied pressure. These two patents are hereby incorporated by reference in their entirety. The padding disclosed in these patents has the disadvantage of being slow to flow in response to pressure, thus having a high shearing force and being prone to cause skin damage. The materials disclosed in these patents also have memory, causing them to tend to return to their original shape after removal of a deforming pressure. The memory of the material causes the material to exert additional pressure on protuberances of the body, such as on bony areas, increasing the risk of tissue damage. Typically, material having memory has a high shear force as well, increasing skin damage during use. Memory is also described in Chris A. Hanson U.S. Pat. No. 5,147,685 issued Sep. 15, 1992, Terrence M. Drew U.S. Pat. No. 5,204,154 issued Apr. 20, 1993, Chris A. Hanson U.S. Pat. No. 4,952,439, issued Aug. 28, 1990, Thomas F. Canfield U.S. Pat. No. 3,529,368, issued Sep. 22, 1970, Terrence M. Drew et al. U.S. Pat. No. 5,093,138, issued Mar. 3, 1992, Chris A. Hanson U.S. Pat. No. 5,058,291, issued Oct. 22, 1991 and Terrence M. Drew et al. U.S. Pat. No. 5,100,712 issued Mar. 31, 1992 each of which is incorporated by reference in its entirety.
Thomas F. Canfield U.S. Pat. No. 3,529,368 issued Sep. 22, 1970 discloses a pad filled with a quickly conforming material, such as elastomeric particles covered with a lubricant (Canfield at column 3, lines 24-29). Canfield does not disclose, however, substantially unrestricted movement of lubricated spherical objects in all three dimensions, as included in Applicant's invention. Canfield also does not disclose the use of a highly lubricous (or friction reducing) lubricant that substantially reduces the coefficient of friction between spherical objects. Canfield also does not disclose a lubricant which is designed not to impede the sliding and rolling of microspheres with respect to each other. Further, Canfield fails to disclose the readily flowing and shearing action of the invented composite mixture in response to deforming pressure exerted on it, the flowing and shearing action being accomplished by spherical objects moving in sliding and rolling contact with each other. It is of note that Canfield's FIG. 4 discloses lubricated elastomeric particles of irregular shape (i.e. not spherical). Objects of irregular shape, even if lubricated, would not achieve low friction sliding and rolling with respect to each other in order to achieve ready flow and shear under pressure. Further, the Canfield elastomeric particles would by nature have memory, a negative attribute that the instant invention strives to eliminate.
Eric C. Jay U.S. Pat. No. 4,728,551 issued Mar. 1, 1988, Jack C. Swan, Jr. U.S. Pat. No. 4,243,754 issued Jan. 6, 1981, Jack C. Swan, Jr. U.S. Pat. No. 4,229,546 issued Oct. 21, 1980, Jack C. Swan, Jr. U.S. Pat. No. 4,255,202 issued Mar. 18, 1981, Jack C. Swan, Jr. U.S. Pat. No. 4,144,658 issued Mar. 20, 1979, Jack C. Swan, Jr. U.S. Pat. No. 4,038,762 issued Aug. 2, 1977, Henry Wilfred Lynch U.S. Pat. No. 3,398,213 issued Oct. 19, 1976, and Frederick L. Warner U.S. Pat. No. 3,748,669 issued Jul. 31, 1973, each of which is hereby incorporated by reference in its entirety, disclose pressure compensating mixtures which are generally characterized by having a quantity of microbeads dispersed in a flowable liquid medium. Disadvantages of such mixtures include their weight, head pressure and memory. The liquid described in those patents is formulated for certain flow characteristics, and the microbeads are merely added because of their low specific gravity to reduce the total weight of the mixture. The resulting mixture is still very heavy because the light microbeads are not used to replace a substantial amount of the heavy liquid, but are instead used only to provide a slight weight reduction of the mixture compared to the use of a liquid alone.
Robert W. Weile U.S. Pat. No. 3,552,044 issued Jan. 5, 1971 discloses a conformable pad filled with elastomeric particles covered with a lubricant (column, lines 34-38). This patent is incorporated by reference herein in its entirety. The elastomeric particles are not round or microspheres and, therefore, do not accommodate a sliding and rolling contact. Rather, the elastomeric particles are made from rods and have flat ends that would interfere with the free movement of particles in Applicant's composite mixture. The irregular shape of the particles provides a high resistance to flow and shear.
Reginald Dyson U.S. Pat. No. 3,968,530 issued Jul. 13, 1976, which is incorporated by reference herein in its entirety, discloses a body support means which is characterized by a relatively viscous fluid and an insoluble filler. The preferred viscous fluid is a gelatin or cellular gelatin material, or a mixture of sodium carboxymethyl cellulose and water. The fluid and filler mixture disclosed in this patent has the disadvantage of being slow to flow in response to pressure, thus having a high shearing force and being prone to cause skin damage. The fluid and filler mixture is also present in an amount which is substantially more than to thinly coat the entire surface of the microbeads and to provide a volume that is substantially more than the volume of the interstitial spaces of the microbeads. The resulting mixture is also heavy because the amount of liquid is substantially more than required to thinly coat the entire surface of the microbeads. The amount of the viscous fluid confers head pressure to the flowable mixture, and the microbeads are not in sliding and rolling contact with each other.
Chris A. Hanson U.S. Pat. No. 4,083,127 issued Apr. 11, 1978, relates to a pressure compensating mixture which is characterized by having a quantity of microbeads dispersed in a flowable liquid medium. This patent is hereby incorporated by reference in its entirety. The preferred flowable material is a mixture consisting essentially of wax and oil, preferably a petroleum based oil, and microbeads. The wax and oil mixture is present in an amount to more than thinly coat the entire surface of the microbeads, and to provide a volume that is substantially more than the volume of the interstitial spaces of the microbeads. The resulting mixture is also heavy because the amount of liquid is substantially more than required to thinly coat the entire surface of the microbeads. The amount and characteristics of the wax and oil mixture confer memory to the flowable mixture, and the microbeads are not in sliding and rolling contact with each other.
Frank D. Werner and Marvin A. Luger U.S. Pat. No. 3,407,406 issued Oct. 29, 1968 relates to a conformable pad which is characterized by having a quantity of microbeads dispersed in a waxy, greasy or oily liquid lubricant such as grease or oil. This patent is hereby incorporated by reference in its entirety. The lubricant causes the microbeads to stick together, and to provide padding that will not change in shape in response to transient or short-time forces. The amount of the lubricant, and the resistance to shape change of the lubricant and bead mixture, confers substantial memory to the flowable mixture, thus having a high shearing force and being prone to cause skin damage. Werner states that a special liquid coating is added to the pad material to cause the small spheres of the pad material to stick together (column 3, lines 6-8; column 7, lines 3-5; column 11, line 31). In contrast with this feature, the present invention uses a lubricant to reduce friction between the spherical objects and to provide maximum movability of the spherical objects with respect to each other in all three dimensions, resulting in a low memory and low shear threshold padding material. The Werner pad will not change shape in response to transient or short-time forces (Werner at column 5, lines 41-43; column 7, lines 38-40). In contrast, Applicant's padding material will deform, shear or change shape in response to the slightest force or pressure, thereby reducing force and damage to body tissue. Applicant's invention has these features because of Applicant's choice of slightly lubricated spherical objects, not spherical objects dispersed in a liquid or gel, and not spherical objects held together with a sticky substance.
Philipp Schaefer U.S. Pat. No. 4,252,910 issued Feb. 24, 1981 relates to a material for resilient, conforming pads, cushions and supports. This patent is hereby incorporated by reference in its entirety. The material comprises elastic, gas-filled microparticles formed into a mass by a thermoplastic bonding agent. The material is semi-liquid at body temperature. One feature of the material is that below body temperature, the material is solid, and therefore, is very resistant to flow under cold conditions. Contour-linings made of such a material were resilient to normal shocks associated with use of the lining. The resistance of the material confers substantial memory to the flowable mixture, thus having a high shearing force and being prone to cause skin damage.
The following U.S. Pat. Nos. relate to cushioning devices and their construction: U.S. Pat. No. 5,163,196 dated Nov. 17, 1992 in the name of Robert H. Graebe et al.; U.S. Pat. No. 5,052,068 dated Oct. 1, 1991 in the name of Robert H. Graebe; U.S. Pat. No. 4,698,864 dated Oct. 13, 1987 in the name of Robert H. Graebe; U.S. Pat. No. 5,111,544 dated May 12, 1992 in the name of Robert H. Graebe; U.S. Pat. No. 5,369,828 dated Dec. 6, 1994 in the name of Robert H. Graebe; U.S. Pat. No. 5,018,790 dated May 28, 1991 in the name of Eric C. Jay; and U.S. Pat. No. 4,953,913 dated Sep. 4, 1990 in the name of Robert H. Graebe. Each of these patents is hereby incorporated by reference in its entirety.
The following U.S. Pat. Nos. relate to filler materials for various devices such as toys and balls: U.S. Pat. No. 5,190,504 dated Mar. 2, 1993 in the name of Mark A. Scatterday; U.S. Pat. No. 5,335,907 dated Aug. 9, 1994 in the name of Donald Spector; U.S. Pat. No. 4,952,190 dated Aug. 28, 1990 in the name of Howard R. Tarnoff et al.; U.S. Pat. No. 3,748,779 dated Jul. 31, 1973 in the name of Cherk et al.; U.S. Pat. No. 4,744,564 dated May 17, 1988 in the name of Yamada; U.S. Pat. No. 3,518,786 dated Jul. 7, 1970 in the name of J.H. Holtvoigt; U.S. Pat. No. 4,256,304 dated Mar. 17, 1981 in the name of Tommy L Smith et al.; and U.S. Pat. No. 4,467,053 dated Aug. 21, 1984 in the name of Richard A. Markle. Each of these patents is hereby incorporated by reference in its entirety.
Background information related to the invention is described in Terrence M. Drew U.S. Pat. No. 5,204,154 issued Apr. 20, 1993, John C. Dinsmoor U.S. Pat. No. 5,201,780 issued Apr. 13, 1993, Chris A. Hanson U.S. Pat. No. 5,147,685 issued Sep. 15, 1992, Adrian Q. Rojas U.S. Pat. No. 5,079,786, issued Jan. 14, 1992, Hubert P. M. Pollmann U.S. Pat. No. 5,079,787 issued Jan. 14, 1992, Eric C. Jay U.S. Pat. No. 5,018,790 issued May 28, 1991, Terrence M. Drew et al. U.S. Pat. No. 5,015,313 issued May 14, 1991, Eric C. Jay U.S. Pat. No. 4,842,330 issued Jun. 27, 1989, Eric C. Jay U.S. Pat. No. 4,761,843, issued Aug. 9, 1988, Eric C. Jay U.S. Pat. No. 4,726,624 issued Feb. 23, 1988, Donald H. Shaktman U.S. Pat. 4,709,431 issued Dec. 1, 1987, Eric C. Jay U.S. Pat. No. 4,660,238 issued Apr. 28, 1987, and Eric C. Jay U.S. Pat. No. 4,588,229 issued May 13, 1986, each of which is hereby incorporated by reference in its entirety.
The following U.S. Patents relate to cushioning pads and mattresses: U.S. Pat. No. 5,103,518 dated Apr. 14, 1992 in the name of Keith Gilroy et al.; U.S. Pat. No. 5,020,176 dated Jun. 4, 1991 in the name of Derek P. Dotson; U.S. Pat. No. 5,010,608 dated Apr. 30, 1991 in the name of Richard I. Barnett et al.; U.S. Pat. No. 4,954,588 dated Aug. 4, 1990 in the name of Daniel G. Cassidy et al.; U.S. Pat. No. 4,292,701 dated Oct. 6, 1981 in the name of John Woychick; U.S. Pat. No. 4,472,847 dated Sep. 25, 1984 in the name of Clifford E. Gammons et al.; and U.S. Pat. No. 3,462,778 dated Aug. 26, 1969 in the name of J. K. Whitney. Each of these patents is hereby incorporated by reference in its entirety.
Prior art bladders, which are typically made of a rubber or plastic film material by processes such as welding of films, rotational molding, or dipping, typically could only contain a liquid filler, such as a glycerin, oil or other liquid, for a period of months before the glycerin, oil or other liquid began to migrate through the bladder wall, causing a mess and changing the properties of the filler in the cushion. An exception to this problem were prior art silicone fluids, which had less tendency to migrate through rubber or plastic bladders. Cushioning products made using silicone fluids are very expensive and heavy, however, which makes them undesirable in light of the present invention. The prior art alternative to silicone fluids was non-fluids, such as petroleum jelly and other very thick compositions that would not flow readily and that had a very high resistance to shear. Of course, neither silicone fluid nor petroleum jelly are easily washable since neither is water soluble, creating clean-up problems whenever such a material is leaked or spilled.
Flotation devices, such as life vests, typically included a flotation material such as foam with small air bubbles throughout its interior. While such flotation material typically had a low specific gravity, it was usually semi-rigid or stiff and was uncomfortable to wear. The stiffness of the flotation material caused flotation devices such as life vests to restrict body movement of the wearer and result in discomfort. When a flotation device is made using the invented composite mixture, flotation qualities approaching the qualities of prior flotation materials are provided, and the deformable, flowable and shearable nature of the composite mixture permits it to respond to movement of body parts quickly and with little resistance, which results in a flotation device which does not restrict movement or activity. The composite mixture of the present invention has a further advantage as a flotation material because it may be inserted into containers of irregular shape and provide the containers with flotation characteristics. No forming of the composite mixture would be required as with prior foam flotation materials.